Method of lining channels

ABSTRACT

A method of lining a channel can be provided which includes the steps of: installing at a work site a roll having wound thereon a rigid or semirigid plastic pipe shaped initially in the form of an approximately round tube and deformed from the initial form to a flat tubular form, paying off the pipe as softened by heating from the roll installed at the work site toward an inlet of the channel to be lined, and folding the paid-off flat pipe in two to a U shape at a position between the roll and the channel inlet. The U-shaped pipe is hardened by forced cooling from outside immediately after the folding step while being restricted in shape, then inserted into the channel while being thus hardened and thereafter restored to the initial form by being inflated with heat and pressure applied from inside, whereby a lining of improved quality can be formed with an improved work efficiency.

TECHNICAL FIELD

The present invention relates to a method of lining channels, and moreparticularly to a method of lining a channel with a rigid or semirigidplastic pipe as a lining material.

BACKGROUND ART

For example, JP-A No. 42220/1989 discloses a conventional method oflining channels. With this conventional method, a rigid or semirigidplastic pipe shaped initially in the form of a round tube is flattened,then folded in two and wound up in a folded U shape on a roll whenproduced in a plant. At a work site, the pipe is inserted into a channelwhile being paid off from the roll in a state softened by heating. Theinserted pipe is inflated by applying heat and pressure thereto frominside for restoration to the round tubular form as shaped initially,forming a lining along the inner surface of the channel with the rigidor semirigid plastic pipe.

According to the lining method described, the pipe is diminished ineffective outside diameter by being deformed to the folded U shape andcan therefore be inserted into the channel if not fully satisfactorily,whereas since the pipe memorizes the initial shape, the U-shaped foldedportion tends to become unfolded as indicated in broken lines in FIG. 6to correspondingly increase the effective outside diameter when the pipeis so softened by heating as to be paid off from the roll, with theresult that the pipe encounters increased resistance when inserted intothe channel, hence a reduced work efficiency. Especially if made ofpolyethylene, the pipe remains somewhat elastic even when softened byheating, consequently exhibiting a marked tendency to restore its shapebefore deformation when released from the restraint of the deformingstep.

Further if the pipe is held wound on a roll in the folded U shape beforeuse, a folding tendency is afforded in the U-shaped folded portion ofthe pipe during the preservation period. The folding tendency partlybecomes a permanent deformation when the pipe is inflated forrestoration, preventing restoration to the form as shaped initially.

Since the bottom part X inside the U-shaped portion of the pipe (seeFIG. 6) is rounded in a direction opposite to the restoration directionY, the rounded part needs to be reversed by inflation for restoration,so that the inflation entails a considerable adverse effect. If thebottom part X has such a folding tendency and when the rounded part isreversed by inflation for restoration, numerous minute cracks are likelydevelop to impair the quality of the lining undesirably.

DISCLOSURE OF THE INVENTION

The main object of the present invention is to provide a method oflining a channel with a rigid or semirigid plastic pipe serving as alining material, wherein the pipe can be inserted into the channel withreduced resistance so as to achieve an improved work efficiency.

Another object of the invention is to diminish a folding tendency in thepipe to the greatest possible extent for use in the lining method topreclude the adverse effect of the folding tendency on the quality ofthe lining.

Other features of the invention will become apparent from the followingdescription.

The present invention provides a method of lining a channel includingthe steps of:

installing at a work site a roll having wound thereon a rigid orsemirigid plastic pipe shaped initially in the form of an approximatelyround tube and deformed from the initial form to a flat tubular form,

paying off the pipe as softened by heating from the roll installed atthe work site toward an inlet of the channel to be lined, and

folding the paid-off flat pipe in two to a U shape at a position betweenthe roll and the channel inlet,

the lining method being characterized in that the U-shaped pipe ishardened by forced cooling from outside immediately after the foldingstep while being restricted in shape, then inserted into the channelwhile being thus hardened and thereafter restored to the initial form bybeing inflated with heat and pressure applied from inside.

According to the lining method of the present invention, the pipe asU-shaped by folding is hardened by forced cooling while being restrictedin shape, so that the pipe can be inserted into the channel with theU-shaped pipe portion closed, accordingly with reduced resistance, hencean improved work efficiency. Since the pipe is U-shaped by foldingimmediately before insertion into the channel, the U-shaped foldedportion exhibits substantially no folding tendency. This eliminates thecause of minute cracking that would otherwise occur when the pipe isinflated for restoration, consequently providing a lining of highquality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall diagram schematically showing an arrangement forpracticing the method of the invention when the work is to be started;

FIG. 2 is an overall diagram schematically showing the method of theinvention while it is being practiced;

FIG. 2-a is a diagram for illustrating a pipe U-shaped by folding andrestricted in shape;

FIG. 3 is a diagram for schematically illustrating how to fold a pipefrom a flat tubular form to a U shape;

FIG. 4 is a diagram in longitudinal section schematically showing theU-shaped folded pipe as inserted in a channel;

FIG. 5 is a diagram in longitudinal section schematically showing thesame pipe as inflated for restoration;

FIG. 6 is a diagram for illustrating the U-shaped folded pipe;

FIG. 7 is a diagram for schematically illustrating a lining formed bythe method of the invention and as slightly deformed to an ellipticalform;

FIG. 8 is a view in section showing a lining pipe developed anew foreliminating the deformation shown in FIG. 7;

FIG. 9 is a view in section showing a lining free from deformation;

FIG. 10 is a diagram for illustrating a flat tubular pipe as inflated toan extent due to shape memory;

FIG. 11 is a view in vertical section showing the flat tubular pipe asdeformed to an excessively flat form by a reduced pressure maintainedinside thereof;

FIG. 12 is an overall diagram schematically showing the method of theinvention while it is being practiced with the flat tubular pipedeformed to an excessively flat form by a reduced pressure maintainedinside thereof;

FIG. 13 is a diagram for illustrating the pipe in the excessively flatform while it is being folded to a U shape;

FIG. 14 is a diagram corresponding to FIG. 2 and showing an exemplarycase wherein a caterpillar pushing-in device is used as means forpushing the pipe into the channel;

FIG. 15 is a side elevation for illustrating the construction of thepushing-in device;

FIG. 16 is a view in vertical section taken along the line 16—16 in FIG.15;

FIG. 17 is a view in vertical section taken along the line 17—17 in FIG.15; and

FIG. 18 is a view in vertical section showing a modification of thedevice shown in FIG. 15.

BEST MODE OF CARRYING OUT THE INVENTION

Embodiments of lining method of the invention will be described belowwith reference to the accompanying drawings. Throughout the drawings,like parts are designated by substantially like reference numerals orsymbols.

FIG. 1 is an overall diagram schematically showing an arrangement forpracticing the lining method of the invention at the start of the work.A plastic pipe 1 serving as a lining material and wound on a roll 2 isinstalled at a work site in the vicinity of a starting shaft b.

The pipe 1 is shaped by extruding a rigid or semirigid polyethylene inthe form of a round tube and has an outside diameter generallycorresponding to the inside diameter of the channel a to be lined, e.g.,to 90 to 100% of the inside diameter of the channel a. The pipe 1 has awall thickness which is suitably determined in conformity with itsoutside diameter from the range of about 1 to about 10% of the outsidediameter, e.g., about 1 to about 30 mm. The polyethylene for use inextruding the pipe 1 is 0.930 to 0.950 g/cm³ in density, 120 to 250kg/cm² in tensile strength and 100 to 130° C. in softening point. Thepipe 1 may be made of other rigid or semirigid thermoplastics.Polyethylene, polypropylene or like polyolefin plastic pipes areespecially desirable since they have flexibility at room temperature andare movable through bends of channels when inserted thereinto.

The pipe 1 is produced by extruding the plastic in the form of a roundtube and thereafter wound up on the roll 2 while being deformed to aflat tubular form.

For lining, the flat tubular pipe 1 as wound up on the roll 2 istransported to and installed at the work site. To render the pipe 1unwindable from the roll 2 in this installed state, the pipe 1 issoftened by being heated by known heating means, for example, heatingmeans for internally passing steam through the pipe as a heat source.

The steam is supplied to the pipe 1 through a supply line 3. The supplyline 3 has one end connected to a steam supply source, e.g., a boiler,and the other end connected to the innermost of wound-up layers of thepipe 1 to supply steam from the supply source to the innermost of thewound-up pipe layers.

The steam supplied to the innermost layer of the pipe 1 passes throughthe pipe 1 from the innermost layer toward the outermost layer, heatingthe pipe 1 from inside during the passage. The pipe 1 as wound up on theroll 2 in a multiplicity of layers can be uniformly heated and softenedfrom portion to portion over the entire length thereof by continuing theinternal heating.

The pipe 1 is thus heated for softening preferably as accommodated in aheat-insulating casing 4 filled with hot air to prevent the dissipationof heat to the atmosphere and uniformly heat and soften not only theinner layer portion of the pipe section but also the outer layer portionthereof. The casing 4 is provided with a supply line 5 for hot air.

The supply of steam to the pipe 1 is discontinued after the pipe 1 hasbeen softened by internal heating with steam to a state permitting thepipe to be unwound from the roll 2. The pipe 1 is paid off toward achannel inlet a1 having an opening in the starting shaft b.

As shown in FIG. 2, the pipe 1 is paid off from the roll 2 by pulling arope 6 connected to the leading end of the pipe 1. The rope 6 extendsfrom the starting shaft b to an arrival shaft (not shown) through thechannel a and has its base end wound up on a winch (not shown) installedat the latter shaft side.

While moving from the roll 2 toward the channel inlet a1, the pipe 1passes through a deformation zone A and then through arestricting-cooling zone B in succession and is treated as specifiedduring the passage as shown in FIG. 2.

While passing through the deformation zone A, the pipe 1 is graduallydeformed from the flat tubular form to a folded U shape and has itseffective outside diameter reduced to a dimension permitting insertionof the pipe into the channel a.

With reference to FIGS. 2 and 3, the deformation zone A has a pluralityof, e.g., four, rolling devices 71 to 74 arranged side by side along thedirection of movement of the pipe 1.

As seen in FIG. 3, the pipe 1 passes between rolls 71 a and 71 b,between rolls 72 a and 72 b, . . . of these rolling devices 71 to 74,and is progressively deformed during the passage and eventually madeinto a U-shaped folded pipe 1′.

The pipe 1 is passed through a heat-insulating duct 10 until the pipereaches the deformation zone A and is deformed within a heat-insulatinghood 11 so that the pipe 1, especially the outer layer portion thereof,is held satisfactorily softened until the pipe 1 is completely deformed.

The interior of the heat-insulating hood 11 is in communication with theinterior of the heat-insulating casing 4 through the duct 10 and holdstherein a heat-insulated atmosphere of hot air flowing in from thecasing 4.

Upon passing through the deformation zone A, the U-shaped folded pipe 1′enters the restricting-cooling zone B, which is provided with a shaperestricting device 8 and a forced cooling device 9. While passingthrough the zone B, the U-shaped folded pipe 1′ is forcedly cooled withits shape restricted.

The shape restricting device 8 comprises a multiplicity of nipping rolls8 a, . . . arranged side by side along the direction of movement of thepipe 1′. While the pipe 1′ passes between each pair of opposed rolls 8a, the U-shaped portion of the pipe 1′ is held between the nipping rolls8 a from opposite sides as shown in FIG. 2-a and has its shaperestricted. Guide rolls 8 b for preventing deflection are provided alongthe row of the nipping rolls 8 a, for example, at the starting end,intermediate portion and terminating end of the row, i.e., at threelocations.

The forced cooling device 9 is provided approximately over the entirelength of the forced cooling zone B and comprises a cooling unit 9 a ofthe cooling water jet type and/or a cooling unit 9 b of the cooling airjet type. FIGS. 1 and 2 show these units as used in combination. Ifforcedly cooled to excess, the pipe 1′ is exceedingly reduced inflexibility, possibly failing to pass through bends of the channel. Forexample when the pipe is made of polyethylene, it is suitable to effectforced cooling to such an extent that the pipe outer surface is given atemperature of 40±10° C. at the channel inlet. To maintain the pipeouter surface in the above temperature range, steam may be passedthrough the pipe 1′ in the coldest season or in a cold climate.

The pipe 1′ is hardened by forced cooling with its shape restricted,whereby the tendency to restore itself to the initial shape iseliminated. Incidentally, when made of polyethylene, the pipe remainssomewhat elastic even in a thermally softened state, exhibiting a strongtendency to restore the undeformed shape upon being released from therestraint of the deforming step, whereas the restoring tendency can beobviated almost completely by forcedly cooling the outer surface withthe shape restricted. Hardening the pipe 1′ in the U-shaped folded shaperemarkably reduces the resistance to be encountered in inserting thepipe into the channel, rendering the pipe insertable more smoothly toachieve an improved work efficiency.

After the pipe 1′ has been completely inserted into the channel a, theterminal pair of nipping rolls 8 a 1 are forcibly moved toward eachother to close the tail end of the pipe 1′ as shown in FIG. 4. A heatingfluid, e.g., steam, is then supplied to the pipe 1′ at the leading endthereof through a heating fluid supply conduit 12 to apply heat andpressure to the pipe 1′ from inside with the steam. When subjected toheat and pressure from inside with the steam, the pipe 1′ is inflatedand restored to the round tubular form as shaped initially, whereby alining comprising the pipe 1 is formed inside the channel a.

The U-shaped folded pipe 1′ is inflated for restoration without lapse ofmuch time after the folding step and therefore before the U-shapedfolded portion develops any substantial folding tendency, so that thepipe can be restored smoothly free of trouble in its entirety includingthe U-shaped folded portion X (see FIG. 6), i.e., the rounded portion tobe reversed. It is therefore possible to preclude minute cracking thatwould occur on inflation and to form a lining of high quality free ofimpairment.

Since the pipe 1 is wound in a flat tubular form on a roll, respectivefolds are formed at opposite edges 1 a, 1 a (see FIG. 3) of the flatportion during preservation. Owing to the folds thus formed, the pipe 1′fails to completely resume the initial round tubular form and isrestored somewhat insufficiently when inflated, affording a lining 1Awhich tends to deform, for example, to an elliptical form althoughslightly as schematically shown in FIG. 7. This tendency becomespronounced when the plastic pipe 1 has a relatively large wallthickness, for example, of {fraction (1/10)} to {fraction (1/25)} of itsoutside diameter.

In this case, the pipe 1 is shaped first in the form of an ellipserelatively close to a true circle as shown in FIG. 8, subsequentlysolidified by cooling and thereafter flattened along the major axis L1in a state softened by heating. The pipe 1 then memorizes the ellipticalform as shaped initially despite flattening, so that when inflated forrestoration, the flattened pipe tends to restore itself to excess in thedirection of the major axis, i.e., beyond a true circle. The excessiverestoring tendency compensates for the insufficient restoration due tothe folds, correcting deformation and forming a round tubular lining 1Afree of deformation as shown in FIG. 9.

The length ratio of the major axis L1 to the minor axis L2 of the pipeof elliptical cross section, if excessively great, leads to excessivecorrection, permitting deformation to an elliptical form undesirably.Accordingly, the ratio of L1 to L2 is suitably determined usually fromthe range of 1.05-1.20:1 with consideration given, for example, to thewall thickness of the pipe 1.

When the flattened pipe 1 is softened by heating so as to be unwindablefrom the roll 2, the pipe 1 which memorizes its form as shaped initiallytends to somewhat expand from a flat state as indicated in broken linesin FIG. 10, hence reduced flatness.

The reduction in flatness due to the shape memory can be obviated bymaintaining a reduced pressure within the pipe 1 to give an increaseddegree of flatness as shown in FIG. 11.

Stated more specifically with reference to FIG. 12, one end of the steamsupply line 3 is connected to a vacuum generator (not shown) through abranch line 3 a to maintain the pipe 1 at a reduced internal pressure,for example, of about 200 to 500 mm Hg after the pipe 1 has beensoftened by heating. The reduced internal pressure then flattens thepipe 1 to excess as seen in FIG. 11. The excessively flattened pipe 1 isfolded to a U shape as shown in FIG. 13, whereby a U-shaped folded pipe1′ can be obtained as compacted. The pipe 1′ can be inserted into thechannel with improved smoothness.

In the case where the lining method of the present invention is to bepracticed over a long distance, for example, of about 50 to about 200 m,as a single work length, the insertion of the pipe into the channelrequires a considerably great force. In such a case, it is desirable touse pushing-in means at the channel inlet side in addition to thehauling means comprising a winch and usually disposed at the channeloutlet side.

For example with reference to FIG. 2, the shape restricting device 8 isusable also as a pushing-in device in this case by positively rotatingthe component nipping rolls 8 a of the device 8 in the direction oftransport of the pipe 1′. However, the nipping rolls 8 a are liable tosomewhat collapse the U-shaped folded pipe 1′ if given an increasednipping pressure, encounter difficulty in assuring the pipe 1′ of shaperetentivity and are therefore inherently limited in nipping pressure,hence difficulty in affording a sufficient pushing-in force, forexample, due to slippage.

FIG. 14 shows a caterpillar pushing-in device M for use as an example ofpushing-in means. As shown in detail in FIGS. 15 to 17, the pushing-indevice M comprises a group of four caterpillar belts 13 which arearranged at an angular spacing of 90 degrees around the U-shaped foldedpipe 1′, for example, on the upper, lower, left and right sides of thepipe, i.e., at four locations. The pair of upper and lower belts 13, 13are arranged on the U-shaped folded portion of the pipe 1′ and onopposite side thereof. The pair of left and right belts 13, 13 arearranged on the respective lateral sides of the U-shaped pipe.

Each caterpillar belt 13 is reeved around a pair of pulleys 14, 14′, runin this state in circulation by the operation of a drive unit 15 mountedon one of the pulleys 14, and turned by the pulleys 14, 14′ to provideinner and outer straight running portions 16 a, 16 b, the inner 16 a ofwhich faces the folded pipe 1′. The upper, lower, left and right innerstraight running portions 16 a cooperate to form the upper, lower, leftand right side walls of a generally rectangular quadrilateral passageway17 (see FIGS. 16 and 17). The U-shaped folded pipe 1′ is confined intothe passageway 17 surrounded by the upper, lower, left and right sidewalls, whereby the shape of the pipe 1′ can be restricted.

The inner and outer straight running portions 16 a, 16 b are supportedon the back side thereof by a pair of inner and outer guide rails 18 a,18 b so as not to slacken during running.

Of the inner and outer guide rails 18 a, 18 b, the outer guide rail 18 bis fixed, while the inner guide rail 18 a is movable. The outer guiderail 18 b supports the inner guide rail 18 a at at least two portionsalong the lengthwise direction thereof by adjusting screws 19, 19 (seeFIG. 16). The inner guide rail 18 a is movable toward or away from thefolded pipe 1′ relative to the outer guide rail 18 b by rotating thescrews 19,19.

As shown in FIG. 16, the outer guide rails 18 b are arranged above andbelow the U-shaped folded pipe 1′ and at left and right thereof, i.e.,at four locations, and are interconnected in this arrangement byconnecting members 20, for example, at an intermediate portion andopposite side portions, i.e., at three positions (see FIG. 15) toprovide a support frame 21 for the caterpillar belts 13. The pulleys 14,14′ arranged at the turning points of each caterpillar belt 13 arefixedly supported by support members 22 (see FIG. 15) on the outer guiderail 18 b in close proximity thereto, and made free from the inner guiderail 18 a.

When the U-shaped folded pipe 1′ is to be paid off and hauled, theadjusting screws 19, 19 are turned to retract each inner guide rail 18 afrom the normal position toward the outer guide rail 18 b, whereby thepassageway 17 surrounded by the inner straight running portions 16 a, .. . are slightly enlarged. The pipe 1′ is inserted through the enlargedpassageway 17.

After the insertion, the adjusting screws 19, 19 are turned to inwardlyadvance the inner guide rails 18 a, which in turn similarly move theinner straight running portions 16 a into pressing contact with theU-shaped folded pipe 1′.

As schematically shown in FIG. 14, the pipe 1′ moves out of thedeformation zone A into the passageway 17 of the pushing-in device M byway of the shape restricting-cooling zone B. The pipe 1′ within thepassageway 17 is held by the straight running portions 16 a of the groupof four caterpillar belts 13 arranged around the pipe, approximatelyover the entire periphery of the pipe as seen in FIG. 16. Accordingly,the folded pipe 1′ is unlikely to collapse in cross sectional shape evenif subjected to an increased nipping pressure and can be paid off andhauled under a great nipping pressure. Moreover, the caterpillar belts13 serving as nipping means afford a great nipping area, enabling theentire belt assembly to give a great paying-off hauling force.

FIG. 14 shows a forced cooling device 9 which comprises an air duct 9 cand a supply portion 9 d for supplying water mist-containing air to theduct 9 c. While traveling through a shape restricting device 8 disposedwithin the duct 9 c, the U-shaped folded pipe 1′ comes into contact withthe water mist-containing air flowing through the duct 9 c, permittingdeposition of the water mist on the pipe 1′. The deposited water mistdeprives the pipe 1′ of heat on vaporization, so that the pipe 1′ can beforcedly cooled by this type of cooling device using a reduced amount ofcooling water.

The pushing-in device M of the foregoing construction holds the U-shapedfolded pipe 1′ from therearound over the entire periphery thereof by thestraight running portions 16 a of the caterpillar belts 13. Thepushing-in device M is therefore usable also as a shape restrictingdevice for the pipe 1′. Accordingly, the shape restricting-cooling zoneB can be dispensed with by providing a cooling fluid injector 23 on thepushing-in device M as seen in FIG. 16.

According to the invention, as shown in FIG. 18, one pair of side walls,e.g., the upper and lower side walls, of the passageway 17 may beprovided by the inner straight running portions 16 a of respectivecaterpillar belts 13, with the other pair of side walls, e.g., the leftand right side walls, by guide rolls 24. A multiplicity of guide rolls24 are arranged side by side along the direction of travel of theU-shaped folded pipe 1′ at each lateral side over a distanceapproximately equal to the length of the inner straight running portion16 a of the belt 13.

The group of guide rolls 24 are supported by a frame 25. Left and rightlike frames 25, 25 are advanced or retracted leftward or rightward bymoving respective handles 26, 26 through screw rods 27, 27 on theprinciple of screw feeding, whereby the distance between the opposedframes 25, 25, i.e., between the opposed groups of guide rolls 24, 24supported by the frames, is adjustable.

The groups of guide rolls 24, 24 hold the U-shaped folded pipe 1′therebetween from the left and right sides to function solely as shaperestricting means. During the travel of the pipe 1′, the guide rolls arerotated by frictional contact with the pipe 1′, acting to diminish thefrictional resistance.

In cross section, the U-shaped folded pipe 1′ confined in the passageway17 is in the form of a slightly vertically elongated rectangle as shownin FIGS. 15 and 16 or substantially in the form of a square in FIG. 18.The square form is most desirable in view of the buckling resistance tobe offered in pushing in the pipe and the bend radius of the folded pipeportion.

What is claimed is:
 1. A method of lining a channel including the stepsof: installing at a work sites a roll having wound thereon a rigid orsemirigid plastic pipe shaped initially in the form of an ellipticaltube and deformed and flattened along the major axis of the ellipticaltube from the initial form to a flat tubular form, paying off the pipefrom the roll as the pipe is softened by heating installed at the worksite toward an inlet of the channel to be lined, and folding thepaid-off flat pipe in two to a U shape at a position between the rolland the channel inlet, the lining method being characterized in that theU-shaped pipe is hardened by forced cooling from outside immediatelyafter the folding step while being restricted in shape, then insertedinto the channel while being thus hardened and thereafter shaped into around tube, which is substantially free of deformation, by beinginflated with heat and pressure applied from inside.
 2. A lining methodaccording to claim 1 characterized in that a polyethylene or otherpolyolefin pipe is used as the plastic pipe.
 3. A lining methodaccording to claim 1 characterized in that the plastic pipe is shaped inthe form of an ellipse and flattened along the major axis of the ellipsewhile memorizing the elliptical form as shaped initially.
 4. A liningmethod according to claim 3 characterized in that the elliptical plasticpipe is 1:1.05-1.20 in the length ratio of the minor axis to the majoraxis.
 5. A lining method according to claim 1 characterized by softeningthe flat tubular plastic pipe by heating, and thereafter maintaining thepipe at a reduced internal pressure to thereby extensively flatten thepipe prior to folding the extensively flattened pipe to a U shape,wherein by a reduced pressure, the walls of the pipe are in contact inan area of bending where the pipe is folded to a U shape.
 6. A liningmethod according to claim 1 characterized in that the U-shaped foldedpipe is inserted into the channel by using a hauling device at an outletside of the channel and using a caterpillar pushing-in device at thechannel inlet side, wherein the pushing-in device comprises a pair ofupper and lower side walls and a pair of right and left side walls, atleast one pair of the upper and lower side walls or the right and leftside walls comprise a pair of caterpillar belts which can be driven, andthe U-shaped folded pipe is supported by the upper, lower, right, andleft side walls and transferred while maintaining the U shape.
 7. Alining method according to claim 6 characterized in that the caterpillarpushing-in device has a passageway for passing therethrough the U-shapedfolded pipe with its shape restricted, the passageway having a pair ofupper and lower side walls and a pair of left and right side walls, eachside wall of at least one of the pairs comprising an inner straightrunning portion of a caterpillar belt, the inner straight runningportions of said one pair being cooperative to nip the folded pipetherebetween from opposite sides, the folded pipe as nipped beingpushable into the channel as the caterpillar belts travel incirculation.
 8. A lining method according to claim 7 characterized inthat the side walls of the pairs each comprise the inner straightrunning portion of the caterpillar belt.
 9. A lining method according toclaim 7 characterized in that each side wall of one of the pairscomprises the inner straight running portion of the caterpillar belt,each side wall of the other pair comprising a multiplicity of guiderollers arranged side by side in the direction of travel of the belt.